A four-stroke reciprocating piston internal combustion engine has a crankcase which is partially filled with a lubricating oil. In one type of engine, a pump circulates the oil under pressure to lubricate different moving parts of the engine. A loss of oil pressure is easily monitored to automatically stop the engine or to alert an operator in the event that there is insufficient oil in the crankcase. In another type of engine, the oil in the crankcase is highly agitated or splashed about to lubricate the moving engine parts. If the quantity of oil within the engine crankcase decreases through leakage or oil consumption by the engine, the engine may be damaged by inadequate lubrication. In smaller engines and particularly single cylinder engines of the type having splash lubrication rather than forced lubrication, the lubricating oil is constantly agitated and some of the oil will be coated on the surfaces within the crankcase. The small size of the crankcase and the constant agitation of the oil makes crankcase oil level sensing extremely difficult during engine operation using prior art techniques. Engines of this type rely upon the operator checking the oil level prior to starting the engine and, if the engine is operated for long periods of time, periodically stopping the engine to check the oil level. Damage to many small engines due to insufficient lubrication could be prevented if reliance on this human factor is eliminated.
For small engines, electronic oil sensors are not practical due to the cost factor. Many small engines are manually started and use a magneto or a capacitive discharge ignition system for generating a signal to operate the ignition system. There is no generator or alternator and battery present on the engine for operating electronic circuits, such as an electronic oil level sensing system if such a system were developed. The cost of adding a generator and battery to a manually started small engine plus the cost of an electronic oil volume sensor may render the engine unsalable for many applications.